JPH0798672B2 - Strontium aluminosilicate glass substrate for flat panel display - Google Patents

Description

The present invention relates to a flat panel display device, and a strontium aluminosilicate glass substrate therefor.

PRIOR ART AND PROBLEMS TO BE SOLVED BY THE INVENTION Two recent technological advances have made the following possibilities obvious and practical for flat panel display devices. That is, (1) preparation of liquid crystals exhibiting improved properties; and (2) production of a surface layer of fine-grained polysilicon.

The development of liquid crystal has advanced to the point where it is technically possible to manufacture a very large information display panel by manufacturing a small color television receiver from liquid crystal. Since liquid crystals inherently exhibit a slow response to electrical signals, a "switch" that responds quickly to electrical stimuli is needed to build an active matrix display. Thin film transistors (TFTs) perform this function.

It is well known that TFTs can be made from single crystal silicon, but the nature of single crystal silicon limits the size of TFTs made from it. It has been found that the fine-grained polysilicon layer deposited on the substrate can be recrystallized into coarse-grained polysilicon by scanning with a heat source such as a laser. TFTs made from coarse-grained polysilicon are T made from single-crystal silicon.
It was found that the electrical characteristics showed only a slight deterioration compared to FT, and that it works extremely well when multiplexing the liquid crystal display.

Coarse-grained polysilicon active matrix displays require a substrate that is transparent, flat, smooth, inert, consistent with silicon for thermal expansion, and capable of withstanding processing temperatures of at least 850 ° C. Therefore, the glass satisfies these requirements if it does not contain alkali metal ions, and has a linear thermal expansion coefficient (25 ° to 300 ° C) of about 30 to 40 × 10 ^-7 / ° C.
C.) and an annealing point of at least 850.degree. C., preferably 875.degree. In order to use the glass sheet manufacturing method described in US Pat. No. 3,338,696, the glass must exhibit a liquidus viscosity of at least 100,000 poise, preferably 250,000 poise or higher. Moreover, it is very difficult to obtain a transparent and homogeneous glass having an annealing point near 900 ° C. in a molten batch at a temperature of about 1800 ° C. or lower. 1800 ° C
Means a practical limit on the molten material used in contact with platinum-rhodium and many refractories used in oxidizing atmospheres. Lastly, a liquidus temperature of no more than about 1400 ° C. is highly preferred to allow glass production using conventional equipment and techniques.

Therefore, the main object of the present invention is to obtain a linear thermal expansion coefficient (25 ° to 300 ° C.) of about 30 to 40 × 10 ⁻⁷ / ° C., an annealing point of at least 850 ° C., a liquidus temperature of about 1400 ° C. or less, at least The purpose is to prepare a transparent, homogeneous glass exhibiting a liquidus viscosity of 100,000 poise and capable of melting at temperatures not exceeding about 1800 ° C.

Glass satisfying the objectives of the present invention have about 9-12% SrO, 9-12%, expressed in mole percent based on oxide.
Al ₂ O _3, and restricted from 77 to 82% of SiO ₂ glass containing no almost in three components of SrO-Al ₂ O ₃ -SiO ₂ system with a composition consisting essentially of alkali metal oxide It was found that it can be prepared from the specified range. The limitation of these composition ratios is
It is extremely critical. Illustratively, if the SrO level is too high, the annealing point will drop below the desired target and the coefficient of linear thermal expansion will rise to an unsatisfactory high value. Conversely, if the SrO content is too low, the glass becomes very difficult to melt, and / or
Or the liquidus temperature rises to an unsatisfactory level. At lower Al ₂ O ₃ concentrations than specified, the annealing point is too low. Al ₂ O ₃ contents above those specified lead to undesirably high liquidus temperatures. When the amount of SiO ₂ exceeds the specified maximum value, the glass becomes very difficult to melt. SiO ₂
If the level is below the indicated minimum, the annealing point will be very low or the liquidus temperature will be very high.

Although it is not possible to accurately convert the composition range expressed in mole percent to the range of weight percent, the approximation for a ternary system expressed in weight percent is about 13-18% SrO, 1
3-18% Al ₂ O ₃ and 66-72% SiO ₂ .

Small substitutions of SrO in the ternary system with MgO, CaO, ZnO, La ₂ O ₃ , and MnO have an undesired effect on the linear expansion coefficient and / or annealing point and / or liquidus temperature of the glass. Therefore, to maintain the desired glass properties,
Only very small amounts of these substances can be added. It is desirable that a strong flux such as an alkali metal oxide be essentially absent.

Substituting a portion of SrO with BaO slightly increases the linear expansion coefficient, and can also significantly reduce the liquidus temperature to a considerable extent without adversely affecting the viscosity of the glass. Therefore, even if BaO is used instead of SrO, the annealing point does not change at all. This BaO performance is of practical significance for changing the thermal expansion coefficient according to the balance of SrO and BaO concentrations and for careful adjustment. Instead of SrO up to 8 mole percent, preferably not exceeding about 6 mole percent BaO
However, when a melting temperature of 1800 ° C. is adopted, BaO volatilization becomes a problem. SiO does not easily volatilize at 1800 ° C.

Further, although more important from the viewpoint of glass melting, when a large amount of BaO is contained, bubbles are generated in the glass. For example, if all SrO is replaced by BaO, it is virtually impossible to produce a glass that is free of any bubbles at melting temperatures not exceeding 1800 ° C. On the other hand, in a laboratory experiment, a glass containing almost no bubbles could be prepared from the ternary SrO—Al ₂ O ₃ —SiO ₂ glass in the above range. Therefore,
Mixing BaO provides the glass with beneficial properties, but its presence makes it more difficult for volatiles to pollute the environment and to melt the glass to good quality.

Comparison of Prior Art with the Present Invention "Area of glass formation in strontium oxide-aluminum oxide-silicon dioxide system" (Kh. Sh. Iskhakov, Uz
b.Khim.Zh. 15 (1), 10-12 (1971)), 25-60% SrO, 5-30% Al ₂ O ₃ , and 35-
Glass consisting of 65% SiO ₂ at 1500 ° -1550 ° for 1-1.5
Preparation by melting for a time is described. The SrO content is clearly far from that of the present invention.

"Preparation of Glass in Strontia-Alumina-Silica System" (Kh. Sh. Iskhakov. Uzb. Khim. Zh., 15 (2), 79-8)
1 (1971)) describes some of the physical properties determined for glasses having compositions within the above references. The glass was found to have a coefficient of thermal expansion of 64 to 97 × 10 ^-7 / ℃. It is stated that as the SrO content increases, the coefficient of thermal expansion increases.

"Glass" (GIZhuravlav et al., Glass, USSR SU 870,3
65, 7 January 1984) is 25-35% S by weight percent.
wherein and rO, 11 to 20% Al ₂ O _3, and 41-63% of the SiO _2,
We have announced the preparation of glasses with higher softening points and special electrical resistivities. Comparing the concentrations, the SrO level is generally higher and the SiO ₂ level is lower than the glasses of the invention.

"Application of glass in which silicon dioxide-aluminum oxide / strontium oxide system is dispersed on niobium substrate by electrophoretic deposition" (GI Zhuravlav et al., Zh. Prikl. Kh)
im. (Leningrad) 54 (7) 1601-4 (1981)) is a niobium part of a high voltage lamp with a protective electrically insulating coating by electrophoretic deposition of glass having a composition within the ranges given in the above references. It describes the application to.

U.S. Pat.No. 4,180,618 discloses the manufacture of electronic devices consisting of a thin film of silicon deposited on a substrate,
Here the substrate is essentially 55-75% Si by weight.
O _2, 5 to 25% Al ₂ O _3, and 9-15% of CaO, 14 to 20%
Of SrO and at least one alkaline earth oxide selected from the group shown in the proportion of 18-26% BaO. The CaO and BaO content is higher than is acceptable for the glasses of the invention. Although a wide range of SrO, Al ₂ O ₃ , and SiO ₂ overlaps with that of the glasses of the present invention, no excellent matrix of properties is found that can ensure composition within the narrowly limited ranges of the present invention, Also, no examples are given which are within the limits of the glasses of the present invention.

Examples Table I shows a number of glass compositions expressed in mole percent based on oxide and illustrates the parameters of the present invention. The actual batch components include any material of oxides or other compounds that, when melted together, convert to the desired oxide in the proper proportions. In the lab experiments shown below, the batch materials were high-purity sand, Al ₂ O ₃ , SrCO ₃ , BaCO ₃ , MgO, CaO, ZnO, Mn.
It consists of O and La ₂ O ₃ .

The batch materials were compounded, ball milled to a uniform melt and packed in platinum or platinum-rhodium crucibles. These batches containing 77% SiO ₂ and below were melted in an electric furnace at 1600-1650 ° C. for 4-16 hours. SiO ₂
Higher content batches start at 1700 ° in a gas oxygen ignition furnace
Melted at 1800 ° C. for 16 hours. In each case, the melt was cast into an iron mold to form circular slabs with a diameter of approximately 30.5 cm (12 inches) and a thickness of approximately 1.9 cm (0.75 inches), and these slabs were immediately annealed. I transferred it to a container. Table IA
Shows the composition of Table I in weight percent based on oxide.

Table II shows some of the physical properties measured on the glasses. The annealing point and strain point expressed in ° C are AS
It was measured according to the beam bending method described in TMC 598. The coefficient of linear thermal expansion in the range of 25 ° to 300 ° C expressed as × 10 ^-7 ° C was confirmed according to ASTM E 228 using a fused silica dilatometer. The internal liquidus temperature, expressed in ° C, is obtained by placing glass in a platinum boat, placing the boat in a furnace with a liquidus temperature and a gradual temperature gradient, and placing the boat in the furnace.
Obtained by holding for 24 hours. The viscosity of the glass at the liquidus line expressed in 10 ⁵ poise was determined using a rotational viscometer while cooling the glass at 2 ° C / min. Ohm ^- DC resistivity, expressed in cm (250 ° C. and 350 ° C.), at room temperature and
The dielectric constant at 1 KHz, the dielectric loss tangent at room temperature and 1 KHz is ASTM
Determined according to the method shown in D 150, D 257, and D 657. Also, 5% NaOH aqueous solution for 24 hours, 5% NaOH
6 hours for aqueous solution and 6 hours for 0.02N Na ₂ CO ₃ aqueous solution,
Immerse each, dip each at 95 ℃, and reduce each weight by mg / cm ²
The chemical durability when expressed by was confirmed by the visual appearance and the weight loss on the polished glass plate. Appearance was indicated with no change, slight frost, and slight cloudiness indication.

Glasses 19 to 28 were melted in an electric furnace at 1650 ° C for 16 hours.
Glasses 25 and 26 were transparent, viscous and free of bubbles.
Glass 20, 22 and 24 were transparent but contained air bubbles. The other glasses were transparent with some air bubbles. The remainder of the exemplary composition is in a gas oxygen furnace.
Melted at 1800 ° C. for 16 hours. Up to 81 mole percent SiO ₂
At the level, the glass was transparent, viscous and free of bubbles. With a SiO ₂ concentration of 82 mole percent, the glass is transparent,
It was very viscous and surprisingly had no air bubbles. At a SiO ₂ content of 83 mole percent, the glass was transparent,
It was slightly moving and viscous and contained some air bubbles.

Examining both Table I and Table II together, it can be melted at temperatures below about 1800 ° C and has an annealing point of at least 850 ° C, 25 ° -300
Linear thermal expansion coefficient of about 30-40 × 10 ^-7 / ℃ in the temperature range of ℃, about 1
Liquidus temperature not exceeding 400 ° C, and at least 100,000
To prepare a glass exhibiting Poise's liquidus viscosity, Sr
The importance of keeping the O, Al ₂ O ₃ , and SiO ₂ concentrations within the defined ternary system is clearly demonstrated. This study also shows the generally unfavorable effect of the incorporation of MgO, CaO, ZnO, La ₂ O ₃ and / or MnO on the glass produced with respect to the above properties. On the other hand, the addition of BaO is effective in lowering the liquidus temperature without seriously affecting the viscosity of the glass.
Attention must be paid to the volatilization of and the generation of bubbles in the glass.

Claims (2)

[Claims] 1. An annealing point of at least 850 ° C., 25 ° to 300
Approximately 30-40 × 10 ^-7 / ℃ linear thermal expansion coefficient, 140 in the temperature range of ℃
It can be melted at a liquidus temperature not exceeding 0 ° C. and at a temperature below about 1800 ° C., which exhibits a liquidus viscosity of at least 1 × 10 ⁵ poise, is essentially free of alkali metal oxides, and is based on oxides. 9-12% SrO, 9-1 expressed in mole percent
Bright transparent strontium aluminosilicate glass consisting essentially of 2% Al ₂ O ₃ and 77-82% SiO ₂ . 2. A glass according to claim 1 in which SrO is replaced by up to 8 mole percent BaO.